https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94181
Bug ID: 94181
Summary: Misidentified dangling reference in container
implementation
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ada
Assignee: unassigned at gcc dot gnu.org
Reporter: simon at pushface dot org
Target Milestone: ---
Created attachment 48035
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48035&action=edit
Reproducer
This arose in a simple implementation of a Container’s Reference function:
type Reference_Type
(Element : not null access Element_Type)
is record
Dummy : Integer := raise Program_Error with "uninitialized reference";
end record;
function Reference
(C : aliased in out Container; Position : in Cursor)
return Reference_Type
is
pragma Unreferenced (C);
begin
return (Element => Position.The_Node.all.The_Element'Access, Dummy => 1);
end Reference;
With GCC 9, this was fine (so long as that .all is in there! Weird). With GCC
10.0.1 20200206 (experimental) (GCC), we get
3. function Reference
4. (C : aliased in out Container; Position : in Cursor)
5. return Reference_Type
6. is
7. pragma Unreferenced (C);
8. begin
9. return (Element => Position.The_Node.all.The_Element'Access,
Dummy => 1);
|
>>> access discriminant in return aggregate would be a dangling
reference
10. end Reference;
This (the same style as used in Ada.Containers) is OK.
function Reference_With_Extended_Return
(C : aliased in out Container; Position : in Cursor)
return Reference_Type
is
pragma Unreferenced (C);
begin
return R : constant Reference_Type :=
(Element => Position.The_Node.The_Element'Unchecked_Access, Dummy => 1)
do
null;
end return;
end Reference_With_Extended_Return;
Randy Brukardt[1] thinks there should be no difference.
[1] https://groups.google.com/d/msg/comp.lang.ada/IUQ6DUe3Shw/wULgGGjqAgAJ
